Was the canopy weeping rather than the standard Ash canopy? If so this could be the result of a graft.

The lowest section would be the root stock of Fraxinus excelsior and the section above the grafted material, Fraxinus excelsior 'Pendula' . This is commonly done with weeping varieties of trees such as Fraxinus, Prunus, Salixetc. The grafted material bulges out because of a different rate of growth in the two parts. Weeping Ash Fraxinus excelsior 'Pendula'was very popular in the Victorian era and as propagating from seed gives unpredictable results, vegetative propagation was, and is, commonly utilised to produce the plants.